In a conventional facsimile, digital copying machine, or the like, to copy an original image at high speed, so-called flow scanning is performed. In this processing, original read operation is performed by sequentially feeding originals placed on the document feeder onto the original table, moving each original under the original table glass, and conveying it on the image reading unit in the ready state at a predetermined speed instead of moving the image reading unit relative to the originals placed on the original table.
An original is read by a CCD or the like. Recently, an original can be read as high-resolution data at a resolution as high as 600 pixels per inch.
Owing to the merit in handling images as digital data, one machine has a facsimile function and has a function of printing data from a personal computer or the like as well as a copy.
In flow scanning, however, since an original image moving on a predetermined position on the original table is read as high-resolution data, data in the form of black or white streaks, which are not present on the original, are formed on a copy sheet due to the influence of abnormal states such as minute dust, dirt, or flaws (a points A and B in FIG. 31).
In addition, in the facsimile transmission mode, data in the form of streaks are transmitted.